EP 1 314 885 discloses a flexible serrated trailing edge of a wind turbine. A serrated panel is connected at the trailing edge of the blade to optimize the aerodynamic characteristics of the wind turbine blade. This results in an increased electrical output power of the wind turbine for example.
The shape of the trailing edge even influences the noise or the aerodynamic noise, which is originated by the wind turbine blade. Thus, the dimension and the shape of a panel, which is attached to the trailing edge, even contribute to the aerodynamic noise of the turning wind turbine blade. Thus a compromise needs to be found between the location and the dimension of the panel for an improved blade-characteristic on the one hand and a reduced aerodynamic noise on the other hand.
FIG. 4 shows a blade 1 of a wind turbine. A number of panels 2 are arranged at and along the trailing edge TE of the blade 1. The panels 2 show a number of serrations SE. the size and the shape of the panels are optimized in a way that a lift-drag-ratio of the blade is increased. Thus, the aerodynamic characteristics of the blade 1 are improved.
The panels 2 might connected by a glue with the trailing edge TE. Thus retrofitting of existing blades in dependency of specific conditions of the site of the wind turbine is quite easy.
The panels 2 may be made in smaller sections and may be attached side by side as illustrated. Thus an entire flap, arranged at the trailing edge TE of the blade, is established or constituted.
FIG. 5 shows a specific detail of FIG. 4, which is indicated by a circle there. The flap FP as shown here in detail comprises several panels 2. This allows a flexible movement of the serrated panels 2 when the wind turbine is in operational mode. Due to the flexing of the serrated panels the blade characteristics are improved.
There is a little gap GP between two adjacent panels 2. The gap GP is needed for the flexing movement of the panels 2. Additionally, the panels 2 are connected with the trailing edge TE by a band or strip or connection-area FX. This connection-area FX is preferably used for a glue-connection.
Another band or strip OL is arranged between the connection area FX and the serrations SE, thus a kind of “overhang” or projection OL is created.
The little gap GP between the panels 2 generates a whistle-tone as aerodynamic noise. The whistle-tone is even influenced by the dimension of the strip OL or overhang OL.
The whistle tone is originated by the wind V, which is slipping through the gap GP. This is schematically shown in FIG. 6.
FIG. 7 refers to the FIG. 5 and shows a well known prior art solution to reduce this whistle-tone.
The gap GP between the panels 2 is filled with a flexible filler material 3. However, the filler material 3 deteriorates over time and becomes stiff and inflexible. Thus the filler material 3 finally might fall off. The usage of the filler material even results in time extensive work thus this solution is expensive.